Diaphragm carburetor for an internal combustion engine

ABSTRACT

A diaphragm carburetor for an internal combustion engine is provided, and has a housing with an impulse pressure driven fuel pump. Provided in the housing is a chamber that is divided by a diaphragm into a pump chamber and a drive chamber that is acted upon by impulse pressure fluctuations during operation of the internal combustion engine. In order with the least available impulse pressure differences of the engine to effectively deflect the diaphragm in the chamber, the freely movable diaphragm surface of the diaphragm is maximized and the conveying stroke of the diaphragm is enhanced by a spring. The movable diaphragm surface assumes a major portion of the surface of the plane of separation in which the diaphragm is disposed. For this purpose, a fuel intake valve and a fuel outlet valve are spaced from the diaphragm, and in particular are removed from the plane of separation in which the diaphragm comes to rest.

BACKGROUND OF THE INVENTION

The present invention relates to a diaphragm carburetor for an internalcombustion engine.

DE 22 55 594 discloses a diaphragm carburetor for an internal combustionengine, according to which an impulse pressure driven fuel pump isdisposed in the carburetor housing. The fuel pump is embodied as adiaphragm pump, the diaphragm of which separates a fuel conveyingchamber or a pump chamber and an impulse chamber or an operatingchamber. The impulse chamber is connected to a source of pulsatingpressure, and the diaphragm is acted upon by a spring that extendsthrough the impulse chamber. At partial vacuum impulses, the diaphragmmoves against the force of the spring, which during a change to pressureimpulses enhances the fuel conveyance in the pump chamber and reinforcesthe fuel conveying pressure of the diaphragm pump. With this knowndiaphragm carburetor, it is not possible to have a disruption-freeoperation, especially in conjunction with an internal combustion enginehaving only weak positive pressure impulses.

It is therefore an object of the present invention to provide adiaphragm carburetor of the aforementioned general type with which it ispossible to have a disruption-free operation of the internal combustionengine even with predominantly negative pressure impulses of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

This object, and other objects and advantages of the present invention,will appear more clearly from the following specification in conjunctionwith the accompanying schematic drawings, in which:

FIG. 1 is a side view of one exemplary embodiment of a diaphragmcarburetor, with a longitudinal cross-section of a fuel pump;

FIG. 2 shows the portion 11 of FIG. 1;

FIG. 3 is an exploded view of the diaphragm carburetor of FIG. 1;

FIG. 4 is a schematic cross-sectional view through the fuel pump with apartial vacuum impulse applied in the pump chamber in a first operatingrange;

FIG. 5 is a schematic cross-sectional view through the fuel pump in asecond operating range; and

FIG. 6 shows the stroke of a fuel pump diaphragm plotted against therelative pressure in the pump chamber.

SUMMARY OF THE INVENTION

The diaphragm carburetor of the present invention comprises an impulsepressure driven fuel pump that is disposed in a carburetor housing andis formed of a pump chamber, an operating chamber, and a diaphragm towhich force is applied by a spring; lateral edges of the diaphragm areheld in a plane of separation between sections of the housing, whereinthe diaphragm separates the pump chamber and the operating chamber; afreely movable diaphragm surface is defined between the lateral edges ofthe diaphragm, which are spaced apart by a distance that in the plane ofseparation is equal to more than half of the width of the carburetorhousing; a fuel intake valve and a fuel outlet valve are associated withthe pump chamber and are disposed at a distance from the plane ofseparation.

In order with the impulse pressure driven fuel pump to be able to effecta reliable fuel conveyance even at predominantly or exclusively negativepressure impulses in the drive chamber of the fuel pump, the movablediaphragm surface of the pump diaphragm is maximized. The surfaceportion, in other words the movable diaphragm surface, that is presentbetween the diaphragm edges that are clamped in the carburetor housingis in particular maximized by having all possible functional elements,especially a fuel intake valve and a fuel outtake valve, be removed outof the plane of separation of the carburetor housing in which thediaphragm is disposed and by having them be disposed at a distance tothe plane of separation in which the diaphragm is disposed.

If a partial pressure impulse acts upon the diaphragm in the drivechamber, due to the large diaphragm surface an adequate return forcethat acts against the force of the spring is effected against thediaphragm. The displacement path of the diaphragm is a function of themagnitude of the partial pressure, i.e. as the partial pressureincreases the spring is tensioned further. The axial extent of the pumpchamber and working chamber make it possible for the fuel pump tooperate in different operating ranges, i.e. with pressure pulses at ahigher or lower pressure level.

The feature of disposing the fuel intake valve and fuel outlet valve ata distance from a wall of the pump chamber in a separate functionalplane of the diaphragm carburetor leads to a simplification of theconstruction of the carburetor. The plane of separation of thecarburetor housing in which the diaphragm comes to rest is preferablyapproximately the same size as a base surface of the carburetor. Thedrive chamber is expediently formed in a housing cover of thecarburetor. Provided on this housing cover is an impulse connector forthe supply of the pressure and partial vacuum impulses. It is expedientto form the pump chamber in a separate component that is connected tothe main body of the diaphragm carburetor. In the installed state of thediaphragm carburetor, the component is disposed as an intermediate piecebetween the housing cover of the carburetor and the main body of thecarburetor. The volume of the pump chamber can thus be dimensioned as afunction of the height of the intermediate piece. The spring serves forthe return of the diaphragm when a weakening partial pressure impulse,or a positive pressure impulse, is encountered. The change in positionof the diaphragm caused thereby thus effects the fuel conveyance. Ahelical spring, especially a compression spring is preferably utilized.The compression spring is preferably disposed in the drive chamber, andin turn is supported against the inner wall of the housing cover as wellas against the diaphragm. Alternatively, it is also possible to embodythe spring as a tension spring or a leaf spring and to dispose it in thepump chamber. A diaphragm plate that comes to rest in a planar manneragainst the diaphragm is preferably disposed against the spring and thediaphragm. The diaphragm plate can be secured not only against thediaphragm itself but also against the spring. The diaphragm platepreferably partially surrounds one end of the helical spring on thatside that faces away from the diaphragm. The spring is therebystabilized in its position transverse to its longitudinal axis, and isheld in an elastic manner.

The fuel intake valve and the fuel outlet valve are preferably disposedin the interface between the intermediate piece and the main body of thecarburetor. In this way, the valves are easy to embody as diaphragmcheck valves having a large open valve cross-section.

The impulse connector at the drive chamber is to be in fluidcommunication with a source of pulsating pressure of the internalcombustion engine. The internal combustion engine can be not only atwo-stroke engine but also a four-stroke internal combustion engine, inparticular a mixture lubricated four-stroke internal combustion engine.In order to tap the pulsating pressure, the crankcase or an intakeconduit for combustion air is suitable as the source on the internalcombustion engine. With a four-stroke internal combustion engine, inparticular a mixture lubricated internal combustion engine, it isexpedient to provide as the source of pulsating pressure the valvehousing, the valve drive housing, the crankcase, or an intake conduitfor the combustion air. In particular with four-stroke internalcombustion engines, the pulsating pressure is in the range of theexternal pressure of the internal combustion engine or of the negativepressure. If an easy to flex elastomeric flat diaphragm is used as thediaphragm of the fuel pump, this facilitates the deflection of thediaphragm. The diaphragm itself is in this connection advantageouslysupported by the diaphragm plate.

In order to compensate for fluctuations of the impulse pressure, andthereby resulting fluctuations of the fuel conveying pressure, it isprovided that the volume of the pump chamber be of such a magnitude thatthe pump chamber serves as an intermediate storage for fuel that isunder pressure.

Further specific features of the present invention will be described indetail subsequently.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings in detail, the diaphragm carburetor 1illustrated in FIG. 1 serves for the preparation of a mixture, such as afuel/air mixture, for an internal combustion engine 2, especially for atwo-stroke engine or a four-stroke engine. Such an engine isadvantageously usable in manually-guided implements such as power chainsaws, brushcutters, trimmers, cut-off machines, lawn mowers, or thelike.

Formed in the diaphragm carburetor 1 is an intake channel 26 via whichcombustion air 27 flows in the direction of the arrow to the intake portof the internal combustion engine. Formed in the intake channel 26 is aventuri section 28, in the region of which open fuel nozzles. Thenozzles are supplied from a control chamber 29 (see FIGS. 1 and 3) inthe interior of the carburetor housing 3. If combustion air flowsthrough the intake channel 26, fuel exits the nozzles and is mixedtogether with the combustion air. The control chamber 29 is suppliedwith fuel from a fuel pump 5 via a feed channel. In the illustratedembodiment, the fuel pump 5 is driven by the fluctuating pressure 25 inthe crankcase 30 of a four-stroke engine 31. For this purpose, a chamber32 of the fuel pump 5 between the housing sections 15, 16 of thecarburetor housing 3 is divided into a pump chamber 6 and a drivechamber 7. These two chambers 6, 7 are separated from one another by adiaphragm 8.

The drive chamber 7 is in fluid communication with the crankcase 30 ofthe four-stroke engine 32, as a result of which pressure fluctuationsare introduced into the drive chamber 7. Alternatingly present at thediaphragm 8 is, for example, a partial vacuum or approximately ambientatmospheric pressure, whereby the pressure fluctuations are a functionof the speed, of the type of internal combustion engine, and of thesource 22 (see FIG. 2) of the pulsating pressure 25 (crankcase, valvehousing, valve drive housing, and intake tube). The pump movements ofthe diaphragm 8 caused thereby effect a fuel feed as a consequence ofvolume alteration of the pump chamber 6 and by means of a fuel intakevalve 9 and a fuel outlet valve 10. The valves are preferably embodiedas diaphragm check valves, ball valves or the like.

The pump chamber 6 is supplied with fuel via the fuel intake valve 9, sothat during the intake fuel flows continuously into the pump chamber.During a subsequent conveying stroke of the diaphragm 8 in the directionof the main body 4 of the carburetor, the fuel intake valve closes andthe fuel outlet valve opens, so that the fuel is conveyed with pressurethrough the feed channel into the control chamber and passes with adefined pressure into the intake channel 26.

As shown in particular in FIG. 2, which is a partial section 11 fromFIG. 1, and in FIG. 3, the diaphragm 8 is embodied as an elastomericflat diaphragm. Provided approximately in the center of the diaphragm 8is a circular disk-shaped movable diaphragm surface or section 11. Thediaphragm section 11 forms a portion of the surface 13 of the plane ofseparation 12 in which the diaphragm 8 comes to rest in the carburetorhousing 3. The surface of the plane of separation 12 is approximatelythe same size as a base surface 24 of the carburetor. The diaphragm 8 isheld between the carburetor housing cover 15 and the intermediate piece16. Between the clamped or held edges of the diaphragm 8, the movablediaphragm section 11 has a span b that corresponds in large part to thewidth B of the carburetor housing 3. In this way there results arelatively large force-engageable surface 11 of the diaphragm 8.

The drive chamber 7 of the fuel pump 5 is formed in the carburetorhousing cover 15, while a recess having a nearly rectangularcross-sectional configuration in the intermediate piece 16 forms thepump chamber 6. A spring 17, which in the illustrated embodiment isembodied as a helical spring 18, is disposed in a spring-clamped mannerbetween the base 33 of the carburetor housing cover 15 and the diaphragm8. A flat diaphragm plate 18 is disposed at one end 34 of the helicalspring 18 between the diaphragm 8 and the spring 18. The diameter of thediaphragm plate 19 is approximately twice as great as the diameter ofthe helical spring 18. The backside of the diaphragm plate 19, whichfaces the helical spring 18, has a sleeve-like configuration, wherebythe wall 37 of the sleeve 38 radially surrounds the end 34 of thehelical spring 18.

The other end 35 of the helical spring 18 is radially held in a recess39 of the carburetor housing cover 15. In this way, the helical spring18 is movably radially held and guided in the drive chamber 7. Insteadof using a helical compression spring, it can be expedient to provide atension spring in the pump chamber. The tension spring can also beembodied as a leaf spring, a plate spring, or a spring blade. It isexpedient to connect the diaphragm plate 19 with the diaphragm 8 in apositive or frictional manner, for example by rivets.

The diaphragm section 11, which is freely movable in the chamber 32,should be as large as possible in order, with the low pressuredifferences that are available especially with four-stroke engines, oralso with the low-pressure differences that are available with atwo-stoke engine, to produce a sufficiently large force during idlingfor the return and biasing of the spring in the drive chamber. For thisreason, in the illustrated embodiment the fuel intake valve 9 and thefuel outlet valve 10 are disposed at a distance a from the functionalplane of the diaphragm 8.

The fuel intake valve 9 and the fuel outlet valve 10 are disposed at thedistance a relative to the plane of separation 12 approximately in aninterface 21 between the intermediate piece 16 and the main body 4 ofthe carburetor. As shown in FIG. 2, for the fluid communication of thepump chamber 6 with the fuel intake valve 9 and the fuel outlet valve10, two orifices 20 are provided in the intermediate piece 16. Thus, inconnection with the available space, the valves can be disposed at anydesired distance from the inner wall 14 of the pump chamber 6. The pumpchamber 6 can be expanded in a desired manner to form a temporarystorage chamber for fuel. As a consequence of these structural features,it is possible to have a compensation of the impulse pressurefluctuations that occur during operation of an internal combustionengine. Fluctuations of the fuel conveying pressure and of the fuelconveying quantity are thereby effectively compensated for. Inparticular, when starting or restarting the internal combustion engine,it is thereby possible to make use of the fuel volume that is alreadyunder pressure in the pump chamber 6. A satisfactory mixture formationis thereby effected in the intake channel 26 of the carburetor 1.

During operation of the fuel pump, pulsating pressure from the source 22is supplied via a connector that is disposed essentially radially in thecarburetor housing cover 15 so as to supply the drive or operatingchamber 7 with a partial vacuum that acts on the diaphragm 8. Under theeffect of the partial vacuum, the diaphragm 8 moves against the springforce of the helical spring 18 with its diaphragm plate 19 in adirection toward the base 33 of the carburetor housing cover 15. By wayof example, FIG. 4 shows that at a certain partial vacuum, for examplein the order of magnitude of about 0.5 bar, the diaphragm 8 isconsiderably deflected against the spring 18. The solid line shows acentral position of a first operating range I, and the dashed lines showthe deflections as a consequence of the pressure pulsations, whereby thepressure amplitude between the deflections is, for example, 0.1 bar. Thediaphragm stroke generated thereby can be approximately 0.25 mm.

FIG. 5 shows that in the region of a different pressure level a secondoperating range II is established. From the base position of thediaphragm 8 illustrated by the solid line, with the spring 18 relaxed,at a partial pressure pulse in the drive chamber of about 0.15 bar thediaphragm 8 is deflected against the spring force. This corresponds tothe lower dashed-line position in FIG. 5. With an attenuation of thepressure pulse there is effected an opposite movement of the diaphragm 8due to the return force of the spring 18 and due to positive pressurepulses, i.e. increasing over the relative normal pressure of 0 bar,there is effected in the drive chamber 7 a deflection of the diaphragminto the upper dashed-line position in FIG. 5.

It is to be understood that between the operating ranges I and IIillustrated in FIGS. 4 and 5 any desired intermediate ranges could alsobe established, or are automatically established due to the respectiveactual pressure level.

A flat diaphragm that is easy to flex is preferably utilized, as aresult of which only slight deformation force has to be applied for thediaphragm itself, and even at the least available pressure impulsefluctuations, a maximum fuel conveying capacity of the fuel pump 5 iseffected.

FIG. 6 is a graph in which the stroke movements of the diaphragm areplotted against the impulse pressure fluctuations generated by aninternal combustion engine, for example in the operating ranges I andII. From this graph it can be seen that the spring characteristic has aproportional path, whereby in the completely relaxed state of the spring18 the diaphragm 8 is in the normal position at 0 mm stroke. Thisposition is assumed at a relative pressure of 0 bar. In the operatingrange II, at a negative pressure impulse of, for example, 0.15 bar, astroke of >0.4 mm is produced against the spring 18. At the end of thenegative impulse, the diaphragm 8 is again in the base position, andwith a subsequent positive pressure impulse there is effected a stroke,as seen in FIG. 6 to the left, of, for example, 0.3 mm. Thus, an overallstroke of 0.7 mm is utilized.

At a pressure level where the overall amplitude is in the partial vacuumrange, as for example in the operating range I, there is respectivelyutilized the rise of the pressure differential to the normal pressure of0 bar for the stroke of the diaphragm 8 against the spring 18, whereasupon reduction of this pressure differential the force of the springacts in the opposite direction and the diaphragm is thus returnedsomewhat. As can be seen from FIG. 6 in the operating range I, atpressure amplitudes of 0.1 bar pump strokes of about 0.25 mm can stillbe achieved, so that with the inventive arrangement even such smallpressure impulses suffice for a required fuel conveyance.

The specification incorporates by reference the disclosure of Germanpriority document 100 64 519.4 of Dec. 22, 2000.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

We claim:
 1. A diaphragm carburetor for an internal combustion engine,said carburetor comprising: a housing having housing sections; animpulse pressure driven fuel pump that is disposed in said housing andis formed of a pump chamber, an operating chamber, and a diaphragm towhich force is applied by a spring, wherein lateral edges of saiddiaphragm are held in a plane of separation between said housingsections and said diaphragm separates said pump chamber and saidoperating chamber, and wherein a freely movable diaphragm surface isdefined between said lateral edges of said diaphragm, which edges arespaced apart by a distance b that in said plane of separation is equalto more than half of a width B of said housing; a pressure impulseconnector that communicates with said operating chamber; a fuel intakevalve associated with said pump chamber; and a fuel outlet valveassociated with said pump chamber wherein both said fuel intake valveand said fuel outlet valve are disposed at a distance a from said planeof separation.
 2. A diaphragm carburetor according to claim 1, whereinsaid fuel intake valve and said fuel outlet valve are disposed at adistance from an inner wall of said pump chamber.
 3. A diaphragmcarburetor according to claim 1, wherein said carburetor has a basesurface, and wherein said plane of separation of said housing isapproximately equal in magnitude to said base surface.
 4. A diaphragmcarburetor according to claim 1, wherein in an orthogonal directionrelative to said plane of separation said pump chamber and saidoperating chamber together have an extent that makes possible adisplacement of said diaphragm into different operating ranges as afunction of a pressure level.
 5. A diaphragm carburetor according toclaim 1, wherein said operating chamber is formed in a cover of saidhousing.
 6. A diaphragm carburetor according to claim 5, wherein saidpump chamber is disposed in a separate component, known as anintermediate piece, that is connected to a main body of said carburetor.7. A diaphragm carburetor according to claim 1, wherein said spring is ahelical spring that is disposed in said operating chamber.
 8. Adiaphragm carburetor according to claim 7, wherein said spring is acompression spring.
 9. A diaphragm carburetor according to claim 1,wherein said spring is a tension spring and is disposed in said pumpchamber.
 10. A diaphragm carburetor according to claim 1, wherein adiaphragm plate is disposed between spring and said diaphragm.
 11. Adiaphragm carburetor according to claim 10, wherein said diaphragm plateis fixedly connected to said diaphragm.
 12. A diaphragm carburetoraccording to claim 10, wherein said diaphragm plate at least partiallysurrounds said spring.
 13. A diaphragm carburetor according to claim 6,wherein said intermediate piece is provided with two orifices for afluid communication of said pump chamber with said fuel intake valve andsaid fuel outlet valve, and wherein in an assembled state of saidcarburetor said intermediate piece, is disposed between said housingcover and said main body of said carburetor.
 14. A diaphragm carburetoraccording to claim 13, wherein at least one of said intake valve andsaid outlet valve is disposed approximately in an interface between saidintermediate piece and said main body of said carburetor.
 15. Adiaphragm carburetor according to claim 1, wherein said operatingchamber is connected to a source of pulsating pressure of a two-strokeinternal combustion engine.
 16. A diaphragm carburetor according toclaim 1, wherein said operating chamber is connected with a source ofpulsating pressure of a four-stroke internal combustion engine.
 17. Adiaphragm carburetor according to claim 1, wherein said diaphragm is aneasy to flex diaphragm.
 18. A diaphragm carburetor according to claim17, wherein said diaphragm is an elastomeric flat diaphragm.
 19. Adiaphragm carburetor according to claim 1, wherein said pump chamber isan intermediate storage for fuel.